The present invention relates to a vehicle seat and, more particularly, to a vehicle seat configured so as to reduce a shock at the time of rear-end collision.
Generally, in a so-called rear-end collision, in which the rear part of a vehicle such as an automobile is struck from behind, or collides heavily when running backward, the head of a passenger on a vehicle seat is tilted to the rear suddenly by an inertial force, and the neck of the passenger may get a shock.
Therefore, conventionally, the seat for a vehicle such as an automobile is provided with a headrest, which supports the passenger's head, above a seat back to protect the passenger's head and neck from a shock caused by rear-end collision and to reduce the shock to the neck.
However, if the headrest is merely provided, the shock to the passenger's body cannot be reduced, and also, in some cases, the shock applied to the neck cannot be reduced sufficiently unless a gap between the passenger's head and the headrest is decreased quickly when a rear-end collision occurs.
To solve the above-described problems, there has been disclosed a technique in which at the time of rear-end collision, the headrest is moved to the front by a rearward movement load of the passenger to support the passenger's head and reduce a shock to the neck (for example, refer to Japanese Unexamined Patent Application Publication No. 2003-341402 (“the '402 Publication”)).
Also, there has been known a technique in which in a vehicle seat provided with a seat back in which a seat back cushion is supported by a seat back frame, an abutting part of the seat back on which the back part of the passenger abuts in rear-end collision has a spring coefficient smaller than that of other parts and a damping coefficient larger than that of other parts (for example, refer to Japanese Unexamined Patent Application Publication No. 2005-028956 (“the '956 Publication”)).
Further, there has been proposed a vehicle seat in which in a seat back having a headrest, a movable frame having a spring body for supporting a cushion material is attached to a fixed frame to which the headrest is mounted in an upper part so that the upper part of the movable frame rotates to the rear around the lower part thereof, and between the fixed frame and the movable frame is provided a spring that carries a usual seating load but permits the movable frame to rotate rearward when an impact load not lower than a predetermined value is applied (refer to Japanese Unexamined Patent Application Publication No. 2000-272395 (“the '395 Publication”)).
Also, there has been known a technique in which both of the right and left sides of a headrest mounting rod are attached to a seat back frame via an upper side link for moving the headrest back and forth (refer to Japanese Unexamined Patent Application Publication No. 2007-062522 (“the '522 Publication”)).
The technique disclosed in the '402 Publication is a technique in which at the time of rear-end collision, the rearward movement of the passenger's chest (upper torso region) is received by a pressure receiving member, and the headrest is moved to the front in association with the rearward movement of the pressure receiving member. In such a technique, to move the headrest in association with the pressure receiving member, a moving mechanism for the headrest must be provided, so that not only the mechanism is intricate and the cost is high, but also a moving part for moving the headrest must be provided on the seat back frame. Therefore, the rigidity must be prevented from decreasing, and the need for increasing the rigidity than usual arises.
In the technique disclosed in the '956 Publication, by decreasing the spring coefficient of the abutting part of seat back on which the back part (“the chest part” in this publication) of the passenger abuts, the rearward displacement of the upper body is increased, and the relative displacement of the head with respect to the back part is decreased. Also, by increasing the damping coefficient by using a low resilience cushion material, the rebound of the upper body is restrained to decrease the relative speed of the head with respect to the back part. Thereby, a shearing force acting on the neck is decreased.
Unfortunately, the technique in which the spring coefficient is decreased and the technique in which the low resilience cushion material is used have a disadvantage that the sinking of the body to the vehicle rear cannot be increased (that is, the displacement cannot be increased).
Also, the technique disclosed in the '395 Publication has an advantage that a working load for rearward movement of a central support part can be predicted with certainty with only setting an elasticity of the spring with respect to the impact load, the central support part always moves rearward, and the operation is certain.
However, the technique disclosed in this publication has a disadvantage that the movability of the movable frame with respect to the fixed frame near the lower part position is very poor, so that all of the seated body cannot sink to the rear side of vehicle because the fixed frame and the movable frame are fixed to each other by a mounting shaft in the lower part. Also, in this publication, since the movable frame is used, the apparatus increases in size as a whole, and therefore this technique also has a disadvantage that it is difficult to reduce the weight.
Also, the technique disclosed in the '522 Publication is a technique in which for the upper side link, one end (rear-end) of a first link rod constituting a part of the upper side link is attached to a movable-side bracket fixed to both of the right and left ends of the headrest mounting rod by a shaft, the other end of the first link rod is attached rotatably to a fixed-side bracket provided above both of the right and left sides of the seat back frame by a shaft, one end of a second link rod is pivotally mounted to the movable-side bracket below the first link bar by a shaft, the middle part of the second link rod is rotatably attached to the fixed-side bracket by a shaft, and further, a plate body is attached to be movable back and forth via wire springs provided in parallel with each other in the up and down direction. In this technique, the tip end of a mounting end part on both of the right and left sides of the wire spring is positioned in front of the plate body in a plan view, so that a large space in which the cushion material can be installed can be provided between the tip end of the mounting end part and the plate body, and the cushioning performance can be improved.
In the technique disclosed in the '522 Publication, however, in order to make the headrest rotatable in a predetermined range, an inhibiting part for regulating the rotation must be provided on the link rod and the like constituting the upper side link. Thus, a link mechanism is formed by using many members including the upper side link consisting of the plurality of link rods. Therefore, this technique has a disadvantage that not only the number of parts increases, but also the link itself increases in size.
The techniques disclosed in the '402 Publication, the '956 Publication, and the '522 Publication have a problem in that a means for transmitting the impact load to the headrest is needed, and the configuration is intricate. Therefore, a technique has been needed in which the construction is simple, the means for transmitting the impact load to the headrest is unnecessary, the side part of the seat back frame is utilized and the degree of freedom in designing is high, and a shock applied to the passenger at the time of rear-end collision can be reduced effectively.
Also, in the technique in which the pressure receiving member (plate body) is attached to the seat frame with a wire, and the headrest is moved in association with the pressure receiving member, the posture is held by the pressure receiving member, and the headrest is moved by a load created in the pressure receiving member, so that the deformation of a wire serving as a connecting member must be prevented as far as possible. Since the wire is not deformed, the sinking amount is hindered. Therefore, this technique has a disadvantage that it is difficult to increase the displacement, and the coexistence with a normal seating feeling is difficult to achieve.
Therefore, there is conceivable a technique in which by using a shock reducing member such as to be in the optimum state under a usual seating load or in rear-end collision, in the case of a technique for attaching an urging element(s) to the shock reducing member, an engagement part such as an engagement pin is formed on the seat back frame as a separate member by welding or the like, an engagement part such as a pin is formed on the shock reducing member as a separate member by welding or the like, and the end parts of the urging element(s) are locked to these engagement parts formed by welding or the like.
In the technique in which the engagement parts are formed by welding or the like as described above, a disadvantage is considered that in addition to the need for using the engagement part such as the pin, which is a separate member, the process for welding or the like is needed, so that the number of manufacturing processes increases.
In particular, in the case where the urging element(s) is disposed to be located in the rear of a side frame constituting a part of the seat back frame, the seat back conceivably has a disadvantage of interference of the urging element(s) itself. In the case where the urging element(s) is located at a rear position of the side frame, a force such as to always rotate the shock reducing member to the rear acts, so that a disadvantage that the normal seating feeling is bad as the seat back for supporting the back surface is present. Furthermore, if the shock reducing member is disposed in the lower part of the side frame, since other members including electric equipment represented by a motor are installed in the lower part of the side frame, a disadvantage that the arrangement of the shock reducing member interferes with the arrangement of other members is present.